We have extended our characterization of the major protein kinase C substrates of 87,000 dalton (Mr 87). We have purified this phosphoprotein to homogeneity. Purified Mr 87 was used to elucidate its amino acid composition, site of phosphorylation and partial amino acid sequence. Polyclonal antibodies to Mr 87 were raised and were used to perform immuno-localization of this phosphoprotein. Cloning of Mr 87 and other studies attempting to elucidate the function of Mr 87 are in progress. Our previous work had demonstrated that protein kinase C is involved in the regulation of receptor activity and neurotransmitter release. This work was further extended. Further characterization and isolation of the 94,000 dalton cyclic AMP-dependent protein kinase substrate was performed.